Out of bounds is a phrase used to describe something that is not allowed or prohibited. There are many synonyms to this phrase, some of which include forbidden, prohibited, off-limits, not permitted, and banned. These words all indicate that an action or behavior is not acceptable or permissible. Other synonyms for out of bounds include beyond the pale, untouchable, taboo, and restricted. The use of these words may vary depending on the context, such as in sports, where the term out of bounds is commonly used, while in more formal settings, phrases like not permitted or prohibited may be used instead.